The field of this invention relates to improving the nutritive value of soybean meal and other proteinaceous feeds for ruminants. More particularly, the invention is concerned with methods of protecting the protein of the feeds from rumen digestion, and with the nutritionally improved feeds resulting from such rumen-protection.
It has been recognized for some time that protein-providing feed materials which are subject to digestion in the rumen are thereby, in effect, downgraded with respect to the feeding value of the protein. It has been proposed that ideally the protein component of the ruminant feed should be "protected" against being solubilized or metabolized in the rumen, passing therethrough in substantially undegraded form, while remaining digestable and metabolizable in the post-rumen digestive system of the cattle or sheep. The development of a practical way for applying this concept to ruminant nutrition has proven difficult. U.S. Pat. No. 3,619,200 proposes the application to the vegetable meal or other proteinaceous ruminant feed material of a rumen resistant coating. The purpose of the coating is to protect the proteinaceous feed from microbial attack in the rumen while decomposing and permitting digestion of the feed within the abomasum and small intestine.
It is also known that the solubility of protein in ruminant feed materials can be reduced by treating the feed materials with tannin, formaldehyde, or other aldehydes. In addition, a reduction in protein solubility can be obtained by heating the protein. These procedures are summarized with literature refrences thereto in U.S. Pat. No. 4,186,213. Feed materials which may be treated by one or more of these procedures to reduce the solubility of the protein in the rumen and to protect against rumen destruction are disclosed as including various vegetable meals.
With reference to feeding value lost by rumen destruction, soybean meal has a relatively low protein efficiency value. See Klopfenstein, Feedstuffs, July, 1981, 23-24. Since soybean meal is one of the major protein-containing feed materials used with ruminants, it is particularly desirable to provide a commercially practical means for protecting soybean meal against rumen destruction while leaving the protein thereof subject to post-rumen digestion and metabolism. For large scale commercial use such a method must be simple, efficient, and of relatively low cost.
I have previously shown that the rumen digestibility of proteinaceous defatted vegetable meals can be reduced by impregnating the feed material with an aqueous solution of a zinc salt, such as zinc chloride or sulfate. (See my published European Patent Application No. 0 107 049.) The impregnated protein material is subjected to moist heat to react the zinc ions with the protein. For example, from 0.25 to 1.3% by weight of zinc (Zn) based on the dry weight of the meal may be incorporated in the vegetable proteinaceous material in the manner described.